French far right party Front National (FN) candidate Marine Le Pen delivers a speech as his father Jean-Marie Le Pen (R) listens, on May 1, 2012 at the Opera square in Paris, during the party's celebrations of Joan of Arc, marking this year her 600th birth anniversary.

With just four days to go before the run-off in France’s presidential election, incumbent Nicolas Sarkozy and Socialist front-runner François Hollande squared off in a raw-nerved television debate followed by millions of riveted French viewers on Wednesday. Yet despite the body checks, rough tackles, and rope-a-dope efforts by the two rivals to take one another out on topics ranging from the euro crisis and tax policies to security and immigration, neither combatant managed to land a blow capable of turning the tables in his favor before the May 6 run-off. But even as Sarkozy fought to reduce the six- to nine-point lead Hollande has in the polls, and Hollande battled to preserve it, another entirely uninvited participant hung over the debate: the formidable figure of National Front (FN) leader Marine Le Pen, who stunned observers by winning nearly 18%—or over 6.4 million ballots—in first-round presidential voting on April 22.

Whether the topic was burqas, voting rights for legal immigrants, European Union policies, Islam in France, or the defense of French values, both Sarkozy and Hollande saw their hand forcibly tipped to take into account the nationalist, protectionist and often xenophobic positions Le Pen has defended in fueling her electoral rise. And even ahead of the nods the two presidential finalists made in her direction at the debate, the 43 year-old daughter of FN founder Jean-Marie Le Pen was relishing the sight of mainstream politicians agonizing over how to reach out to the voters of a political pariah too popular to ignore.

“Many of our supporters don’t understand the scorn of (traditional politicians) who attack the National Front’s values, beliefs and leaders even as they seek the votes of people who backed me,” Le Pen told a gathering of journalists in Paris on Wednesday, promising that her first-round success was just the beginning of far bigger things to come. “I believe we will one day be in power, because one day our views and ideals will be those of the majority in France. Our ideas are gaining ground very rapidly, as we’ve now seen.”

If Le Pen had her way, neither Sarkozy nor Hollande would get any of her first-round votes in the run-off. To press that point, Le Pen said Tuesday she’d cast a blank vote in the run-off, though she advised her backers to vote “with your heart and conscience.” For anyone laboring with that decision, Le Pen offered guidance by using her sharpest verbal knives against the conservative Sarkozy and his ruling Union for a Popular Majority (UMP) party. She has an objective in mind. As pressures mount within the UMP ahead of what she anticipates will be Sarkozy’s defeat, Le Pen expects the centrist and harder-right factions in the president’s party to burst apart upon his fall. “Nicolas Sarkozy’s defeat will be the result of his failure to fulfill a single of the many [campaign promises] he made in 2007… [and] will cause the UMP to implode,” Le Pen predicts. “It’s made up of people who don’t share the same ideas, objectives or ideals. It’s nearing its end.”

That’s a heady forecast, but there are reasons for Le Pen’s swagger. Even prior to her first-round performance, Sarkozy’s overt attempts to woo Le Pen’s backers by defending issues dear to the extreme-right sparked protests from opponents—and consternation even within the UMP. That alarm has risen since the April 22 vote, as other UMP officials have broken with the traditional taboo of reaching out to FN supporters. The most recent example came on Wednesday when Defense Minister Gérard Longuet told an FN-allied publication “there’s a notable difference between Marine Le Pen and her father”—notably that the younger Le Pen champions far-right positions without resorting to the racially-inflaming and anti-Semitic language of her father. That, Longuet contends, makes Le Pen “an interlocutor who, while not being benign, at least isn’t off limits.”

Hollande reacted to the characterization of Le Pen as a legitimate potential UMP partner by calling for Longuet’s cabinet ouster. More surprising was the protest from Sarkozy’s own forces. Government spokeswoman and Budget Minister Valérie Pécresse contradicted Longuet’s comment by stating “No, I don’t believe Marine Le Pen is more an interlocutor than her father.” Similarly, Foreign Minister Alain Juppé noted, “Mr. Longuet speaks only for himself with such statements, which I in no way share.” Those clashes and similar ones before it demonstrate how touchy a matter dealing with a surging Le Pen is for French conservatives—and how Le Pen herself feels the differences in the party working to her favor.

“The declarations against Mr. Longuet by UMP leaders is probably the best way to ensure Mr. Sarkozy’s defeat,” Le Pen said Wednesday. “Millions of voters hear them and either don’t understand them, or feel insulted by them.”

Her first-round result—and the new respect expressed for Le Pen’s talents even by voters who say they abhor her political views—has convinced the FN leader she’s achieved her stated goal of “de-demonizing” her party and those who back it. That, she believes, leaves her on the very threshold of obtaining the legitimacy the FN has always been denied by mainstream politicians. That view was made clear during her annual May Day rally, when Le Pen told backers that a movement commanding nearly one vote in five cast in the first round couldn’t be written off as marginal, extremist or untouchable any longer.

“What’s the effect on you from moving from the role as the idiot who votes for Marine Le Pen to the one of king-maker in the presidential election?” Le Pen asked an estimated crowd of 8,000 supporters. “(And) to move from the status of racist, fascist, and xenophobe to that of a French citizen with real concerns, (and) whom must be spoken to?”

More importantly, which king will Le Pen’s first-round backers crown? Analysts say Sarkozy will need to lure more than 80% of those voters to his side in the run-off—a tall order against polls indicating that less than 50% are planning such a move. Le Pen herself believes 45% of her supporters will vote for Sarkozy, 15% will back Hollande and 40% will abstain or cast blank ballots like hers. Whatever the final numbers are, she warns, her first-round result will not only readjust the electoral balance across France’s political landscape, but also alter the FN’s wider profile to one she now claims to project.

“I refuse the description of ‘extreme-right,’ which is a discriminatory term used by political rivals and certain media to cast the FN as marginal and untouchable,” Le Pen says. “I describe us as patriotic, nationalist and even populist in the sense of being attuned to the concerns of the people, and popular as a result.”

Le Pen’s rising popularity is indeed one thing neither Sarkozy nor Hollande contested in their debate—even as they sought to turn it back or tap into it.